Texturing the surface of plastic extrusions is often difficult and may interfere with the extrusion process. Typically, texturing is performed as a separate process step after the extrusion step.
U.S. Pat. No. 4,671,913 to Gen et al. describes feeding an extruded sheet through cold press rolls followed by guide rolls, and then through embossing rolls.
U.S. Pat.No. 5,164,227 to Miekka describes a method for decoration of a paper or plastic sheeting where the coated sheet is heated to soften the coating and then decorated using embossing rollers to decorate the sheet. A remote heat source softens the sheet before embossing. The surface of the embossing roller is hard and distorts the sheet.
For many extrusions, especially hollow extrusions, textured wheels tend to deform the surface and distort the profile itself. The profile requires support from the underside to resist the force of the wheels. Typically, the texturing wheel also has to provide sufficient cooling to the plastic surface so that the pattern is not diminished by subsequent operations such as calibrating. Texturing wheels or rollers also have an undesirable short repeat pattern which tends to be aesthetically objectionable. Use of rollers also requires that the surface speeds of the roller matches the surface speed of the extrudate so as to further complicate the mechanism.
U.S. Pat. Nos. 4,906,170 to Nelson et al and 5,184,152 to French describe an apparatus for printing, but not texturing, on plastic tubing which might be drawn from an extruder.
Hence, it desirable to provide for an improved apparatus and process for texturing a continuous extrusion with an extended or random pattern without applying undue pressure to the surface of the extrusion.